> Sure, if you like being constantly fatigued and stupid and have a constantly decaying body, you can strip all carbs from your diet. I'm not sure you can survive this; is there any evidence to the contrary?

You mean, is there any evidence aside from every person who manages their diabetes through diet alone? Or the various pre-industrial human cultures who ate virtually nothing but fish and small game because their climate was notoriously resistant to agriculture and fruit trees?

> It's also wildly unhealthy if you don't have fat to burn. Only obese people should engage in that sort of diet.

You seem to be confusing the ketogenic diet with starving. That's not how it works. If you deplete your fat body's stores and get hungry, you simply eat some fat and then your body will burn it for fuel. If you decide to eat much more fat than your body needs, your body will store the fat as fat. But it won't do it quite as readily as with sugar/carbs, and you won't get food cravings mere hours after eating.

> Or the various pre-industrial human cultures who ate virtually nothing but fish and small game because their climate was notoriously resistant to agriculture and fruit trees?

We have longer life span. We are healthier then them. And we have also bigger muscles for those fitness oriented.